For the manufacturing of low density, high performance EPDM foams (sponge), higher double-bond content is generally required (for example, 5-ethylidenenorbornene (ENB) content over 7.5%) for faster curing and higher ultimate crosslink density for improved cellular foam structure and improved mechanical properties, such as compression set resistance. However, high levels of ENB increase the cost of the EPDM rubbers, since the ENB is an expensive raw material. In addition, interpolymers containing high levels of ENB result in cured, shaped formulations with short scorch times, which lead to processing problems.
Alternatively, EPDM rubbers with high molecular weight are often used to improve melt strength and foaming control during foam production. However, high molecular weight EPDM often exhibits poorer processibility, leading to difficulties in mixing with other additives, higher extruder torque and high tendency for melt fracture at the surface of the fabricated articles.
There is a need for a rubber composition comprising an ethylene/α-olefin/non-conjugated diene copolymer rubber, which contains low levels of diene, exhibits superior processibility, produces formed products with excellent surfaces, and has excellent mechanical characteristics, low water absorption, and superior low and high temperature properties.
U.S. Pat. No. 6,777,502 discloses coupled polymers prepared by a process comprising heating an admixture containing (1) at least one polyolefin comprising ethylene and optionally at least one comonomer, and (2) a coupling amount at least one poly(sulfonyl azide), to at least the decomposition temperature of the poly(sulfonyl azide), for a period sufficient for decomposition of at least 80 weight percent of the poly(sulfonyl azide), and sufficient to result in a coupled polymer. In particular, the polyolefin is the product of the polymerization of ethylene, and optionally at least one other alpha-olefin, in the presence of a single site catalyst. However, the polymers (low molecular weight and/or broad molecular weight distributions) cannot be used to form foams with good compression set and low water absorption because of limited melt viscosity and elasticity to support closed-cell foam and limited crosslinking efficiency. Typically, an ethylene/α-olefin/non-conjugated diene interpolymer with high molecular weight and narrow molecular weight distribution exhibit higher crosslinking efficiency, and is preferably used to form a good crosslinked foam structure. See also U.S. Pat. No. 6,528,136.
U.S. Pat. No. 6,506,848 discloses a process for preparing a coupled polymer comprising heating an admixture containing (1) at least one elastomer comprising ethylene and at least one comonomer, which is selected from alpha olefins having at least three carbon atoms, dienes and combinations thereof, and (2) a coupling amount at least one poly(sulfonyl azide), to at least the decomposition temperature of the poly(sulfonyl azide), for a period sufficient for decomposition of at least 80 weight percent of the poly(sulfonyl azide) and sufficient to result in a coupled polymer having a gel content of less than 2 weight percent. However, the polymers (low molecular weight and/or broad molecular weight distributions) cannot be used to form foams with good compression set and low water absorption. See also U.S. Pat. No. 6,376,623.
U.S. Pat. No. 6,552,129 discloses a process of reacting a poly(sulfonyl azide) with a polymer comprising the following steps: (a) forming a first admixture of a first amount of a first polymer or in a liquid which does not require removal from the polymer and a poly(sulfonyl azide); (b) then forming a second admixture of the first admixture with a second amount of at least one second polymer; and (c) heating the second admixture at least to the decomposition temperature of the coupling agent, for a time sufficient to result in coupling of polymer chains. However, the polymers (low molecular weight and/or broad molecular weight distributions) cannot be used to form foams with good compression set and low water absorption. See also U.S. Pat. No. 6,143,829.
U.S. Pat. No. 6,325,956 discloses a process comprising (a) forming a polymeric admixture including at least one polyolefin which has been prepared using a single site catalyst and at least a crosslinking amount of at least one poly(sulfonyl azide) crosslinking agent; (b) shaping the resulting admixture; and (c) heating the resulting shaped admixture to a temperature at least the decomposition temperature of the crosslinking agent. The compositions are fully crosslinked which limits further formulation flexibility with other thermoplastically formable polymers and other additives in forming new shaped articles.
U.S. Pat. No. 5,869,591 discloses a thermoset elastomer comprising a crosslinked pseudorandom or substantially random interpolymer comprising: (a) from 15 to 70 weight percent of monomer units derived from at least one α-olefin, (b) from 30 to 70 weight percent of monomer units derived from at least one vinylidene aromatic compound, and (c) from 0 to 15 weight percent of monomer units derived from at least one diene. The compositions are fully crosslinked.
Additional rheology modified, crosslinked and/or polymer blends are disclosed in the following: International Publication Nos. WO 00/26268 and WO 2006/065651; and U.S. Pat. Nos. 7,199,189; 6,531,546; 6,319,998; 6,040,351; 5,973,017; 5,229,478; 5,242,971; and 4,722,971.
As discussed above, there is a need for EPDM-based formulations, which contain relatively lower levels of ENB, and which have cure rates similar to formulations containing higher ENB interpolymers. There is a further need for crosslinked foams that can be formed from formulations that have longer scorch times. There is yet another need for EPDM-based formulations with improved processibility in ease of mixing, lower extruder torque and improved surface aesthetics due to reduced tendency for melt fracture.
There is also a need for an ethylene/α-olefin/non-conjugated diene copolymer rubber composition capable of producing foamed, vulcanized rubber articles with excellent cellular structure control, thermal and mechanical properties, and improved water repellency. There is a further need for foamable articles that can be made via extrusion, compression molding, injection molding, and other processes. These needs and others have been met by the following invention.